COLL 412 |
| Michael W. Deem, Departments of Bioengineering and Physics & Astronomy, Departments of Bioengineering and Physics & Astronomy, Rice University, 6100 Main Street - MS 142, Houston, TX 77005-1892 |
| Using an atomic-scale model for silicate solutions, the nucleation process during zeolite synthesis in the absence of a structure directing agent is investigated. Monte Carlo schemes are developed to determine the equilibrium distribution of silicate cluster sizes within the context of this model. How the nucleation barrier and critical cluster size change with Si monomer concentration is discussed. Distance and angle histograms as well as ring size distributions are calculated and compared with known zeolite structures. The free energies of critical clusters are compared with those for small clusters of alpha-quartz. The barriers to nucleation is estimated to be on the order of 100 kT, and the critical cluster size is estimated to be between 25 and 50 silicons. The smooth distribution of ring sizes suggests the cluster is amorphous up to 200 silicons. We also survey the size and flatness of rings that occur in known zeolites and also in a set of hypothetical structures. The results suggest that 16-membered rings, while rarely observed in zeolites, are not unique and should be thermodynamically accessible. |
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Ipatieff Award Symposium Honoring Raul Lobo
8:30 AM-11:30 AM, Wednesday, March 31, 2004 Marriott -- Grand Ballroom K, Oral
Division of Colloid and Surface Chemistry |